Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a first image of a display screen or portion thereof with transitional graphical user interface showing our new design; and,

FIG. 2 is a second image thereof.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1-2. The process or period in which one image transitions to another in each sequence forms no part of the claimed design.

The outermost broken lines in the figures show a display screen or portion thereof and form no part of the claimed design. The remainder of the broken lines in the figures show portions of the graphical user interface and form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 